The present invention relates generally to expansion joints for pipelines to compensate for thermal expansion, pressure differentials and lateral movement.
Bellows-type expansion joints are commonly used in the chemical, oil, power and other industries involving extensive piping systems, in order to absorb axial and lateral movements without transmitting excessive thrust to the piping. One known bellows-type expansion joint comprises two outer or end bellows of equal diameter and a central balance bellows of larger diameter than the end bellows. Each outer bellows is connected to the central bellows by tie rods. Under pressure from the medium in the pipes, thrust forces develop in the flexible bellows elements. The forces in the outer and central bellows act in opposite directions, so that it is possible to balance the forces in the expansion joint. Since the bellows are connected by tie rods or fixed bars, which must remain parallel, any angulation in one bellows as a result of lateral movement of the adjacent pipe will be transmitted to the tied bellows. This results in transmission of high forces to the piping system, low bellows lifetime, and restricted total offset capability as a result of the risk of shearing the bellows.
In U.S. patent application Ser. No. 07/874,410 of Francis, filed Apr. 27, 1992, now U.S. Pat. No. 5,248,170 issued Sep. 28, 1993, an expansion joint is described in which opposite ends of the central bellows tied to the respective opposite end bellows by link members which are pivotally secured to the outer ends of the end bellows and tied rigidly to the ends of the central bellows. This allows the end bellows to angulate but prevents transmission of the angulation to the central bellows. This leaves the central bellows free to perform its main function of allowing the expansion joint to absorb axial displacement without transmitting thrust loads to the system. However, this joint allows angulation about one axis only, and thus will absorb lateral offsets in one axis or plane only.